Thickened slurries are favoured for the transport of particulate solid streams in mining and mineral processing. Benefits include reduced water consumption and reduced impact on the environment, and the greater ease of turn down and restart operations. Processes involving the conveyance of high viscosity materials are also found in a variety of other industries, for example the pumping of concrete in the construction industry, crude oil in the oil industry, fly ash in the power industry, and in food and pharmaceutical preparations. The viscous fluid may consist of a single phase or multiple phases.
The benefits however come with a cost since the increased friction loss arising with increasing viscosity elevates pressures and power requirements for conveying viscous materials. Sometimes the pressure required is so high that the capital cost for pumping equipment and the operating energy cost become unacceptably high.
To address these issues, there have been a number of proposals for reducing friction between viscous fluid flows and the conveying conduit, by injecting a lubricating fluid, often water, in an attempt to form a lubricating film between the viscous fluid flow and the wall of the conduit. For example, U.S. Pat. No. 5,361,797 discloses a system for injecting a lubricating fluid such as water, an oil or a polymer solution into the conduit interior from an annular reservoir via a thin circumferential slit that is inclined to direct the lubricating fluid in the direction of slurry flow. The lubricating fluid is delivered in turn to the reservoir through one or a number of feed ports. Tests have shown that the delivery of the lubricating fluid from the circumferential slit is significantly non-uniform resulting in uneven film distribution about the viscous flow and a circumferentially variable downstream effect of the lubrication. These difficulties are likely to be amplified in the arrangement of U.S. Pat. No. 5,605,174 in which lubricating fluid is delivered to the interior of a pipe section via drilled radial holes.
The peripheral unevenness of lubricant injection in these arrangements can be partially offset by increasing the volume of lubricant delivered at the injection station. In typical systems employing water as the lubricating fluid, the resulting proportionate total addition of water, especially where a number of devices are provided over a longer pipeline, may be unacceptable and detrimental to the process, or simply so high as to offset the potential advantages of employing the thickened slurry or viscous fluid as a means of transport.
The present applicant's international patent publication WO2011/050405 discloses a system for reducing friction of viscous fluid flowing in a conduit in which a lubricating fluid is passed under pressure through a porous conduit that defines a portion of the passage guiding the flow. While this configuration is initially effective in delivering lubricating fluid in a peripherally uniform manner, and is therefore suitable for many applications, some applications require the use of suitably treated water to avoid longer term clogging of the conduit pores by finer particles that are inevitably present in the available water supply.
It is an objection of this invention to achieve effective lubrication of a viscous fluid flow in a conduit in a manner that is peripherally substantially uniform but preferably does not entail a potential additional requirement for pre-treated lubricating fluid.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.